The critical period for vocal learning is a developmental characteristic shared by both humans and certain songbirds. The central nervous system (CNS) is known to undergo several changes that are associated with the closure of the critical period, specifically the formation of extracellular matrix (ECM) components known as Perineuronal nets (PNNs). The closure of the vocal learning critical period in the zebra finch results in a highly stereotyped song that remains unchanged for the life of the bird. Therefore, PNNs are linked to a decrease in song variability and neural plasticity; so does destruction of PNNs reopen the critical period? Destruction of PNNs, by using the enzyme chondroitinase ABC, has been shown
to reopen the critical period for some sensory systems, but such a relationship has
not been found in more complex sensorimotor systems like the zebra finch song system. Evidence of a role in social modulation of song has been found for PNNs in the zebra finch song system. This paper describes other studies involving the PNN and neural plasticity, and an experiment that found a partial return to plasticity in the song system through destruction of PNNs coupled with social experience.